1. Field of the Invention
The present invention relates to micropumps and in particular to their use in an integrated circuit cooling device.
2. Discussion of the Related Art
A known cooling device is a metal heat sink placed against a surface of an integrated circuit chip. The carrying off of the heat from a “hot” area of the circuit to the heat sink is performed through a portion of the circuit generally exhibiting poor thermal conductivity.
As a complement to such a heat sink, or if no other cooling device is present, the integrated circuit is placed in an enclosure comprising a blower generating a permanent air current around the circuit.
These two cooling devices, associated or not, may not provide sufficient cooling down of a circuit having a high active density of components.
An object of the present invention is to provide a cooling device capable of maintaining at an acceptable level the temperature of an integrated circuit comprising a large number of active components.
A more general object of the present invention is to provide a micropump.
To achieve this, the present invention provides a pump comprising: a cavity formed in an insulating substrate, the upper portion of the substrate located in the vicinity of the cavity forming a border, a conductive layer covering the inside of the cavity all the way to the border and possibly covering the border, a flexible membrane, formed of a conductive material, placed above the cavity and bearing against the border, a dielectric layer covering the conductive layer or the membrane to insulate the portions of the conductive layer and of the membrane which are close to each other, at least one ventilating duct formed in the insulating substrate which emerges into the cavity through an opening of the conductive layer, and terminals of application of a voltage between the conductive layer and the membrane.
According to an embodiment of the above-mentioned pump, said cavity has substantially the shape of a cup such that the interval between the conductive layer and the membrane progressively increases from the border to the bottom of the cavity.
According to an embodiment of the above-mentioned pump, the membrane is in an idle state when no voltage is applied between said terminals, the application of a voltage deforming the membrane by drawing it closer to the conductive layer, the removal of the voltage bringing the membrane back to its idle state.
According to an embodiment of the above-mentioned pump, the pump comprises a single ventilating duct emerging substantially at the bottom of the cavity.
According to an embodiment of the above-mentioned pump, the pump comprises two ventilating ducts, one emerging substantially at the bottom of the cavity, the other one emerging close to the border.
According to an embodiment of the above-mentioned pump, the pump is connected to an assembly of ventilating ducts formed in the semiconductor substrate of the integrated circuit.
The present invention also provides a method for forming a pump in an integrated circuit, comprising the steps of: forming a cavity in an insulating substrate, the upper portion of the substrate located in the vicinity of the cavity forming a border; covering the inside of the cavity all the way to the border and possibly the border with a first conductive layer; forming an opening of the conductive layer emerging into a ventilating duct previously formed in the insulating substrate; filling the cavity with a sacrificial portion; covering the sacrificial portion and the portion of the first conductive layer placed above the border with a first insulating layer and with a second insulating layer; forming a small opening in the second conductive layer and in the first insulating layer; removing the sacrificial portion; and covering the second conductive layer with a second insulating layer to close back the opening.
According to an embodiment of the present invention, the step of forming a cavity in an insulating substrate comprises the steps of: forming insulating pads on a first insulating layer; covering the first insulating layer and the insulating pads with a second insulating layer; and performing a chem.-mech. polishing of the second insulating layer to expose the insulating pads, the etch method of the polishing being such that it etches the second insulating layer more than the insulating pads, the insulating pads forming said border.
The present invention also provides a method for actuating a pump such as described hereabove, in which a voltage is applied at regular or irregular intervals between said terminals.
The foregoing object, features, and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, in which: